Research On Control Strategy Of Single-phase Non-insolated PV Grid-connected Inverters

Harmonic elimination is still a grave problem in grid-connected photovoltaic systems,and current control strategy is applied to solve this problem efficiently.The research object of this paper is the control strategy of single-phase non-insolated photovoltaic(PV)grid-connected Inverters.Based on the research object,we further study on how to eliminate the harmonic component and improve the quality of grid-connected current.First,several critical technologies of photovoltaic grid-connected inverter are introduced briefly,especially the isolation type inverter topology.And the inverter of ZCT-H6(Zero-Current-Transition H6)bridge inverter topology is ultimately adopted since it has low leakage current and high efficiency.Secondly,the working principle and performance of PR controller are introduced in detail.The short of PR controller are small bandwidth and low frequency compensation,which are improved by adding damping coefficient and phase compensation.Although this method could avoid the above problems,but they also increase the degree of the closed-loop anomalous peaks and increase the difficulty to design the compensate phase angle.It is worth mentioning that first-order digital differentiator is employed in VPI controller,which can eliminate phase delay.And P+VPI controller is well combined with the advantage of VPI controller and PR controller,such as high compensation harmonic frequency and response speed.So the research in this paper are focused on P+VPI controller.The Nyquist diagram is a powerful tool for measuring and optimizing the actual proximity to instability,and it is more suitable than Bode plots to analyze complex systems in which the magnitude and phase curves may cross,respectively,0d B or 180 deg several times.So the method is used to avoid the closed-loop anomalous peaks and analyze the influence of each freedom degree on the plots.So an novel control strategy are purposed in the end which are meet the qualification of the study.Finally,the validity of the new inverter is verified on Matlab/Simulink.